1. Field of the Invention
This invention relates to a band-stop filter using coxial resonators to stop undesired wave, which is applied to a radio communication apparatus.
2. Prior Art
Prior art band-stop filters as shown in FIG. 5(a) (b), comprise resonator units each of which have a end-shorted coxial resonator 1 and a variable condenser 2 for adjusting frequencies connected in series therewith. Printed circuit board 3 combines the resonator units in a multistage configuration, having a hole 10 adjacent bushing 4 which isolates an inner conductor of end-shorted coaxial resonator 1 from the printed circuit board 3. A screw holder 9 is soldered to the printed circuit board 3. Adjusting screw 6 is threaded into and held by screw holder 9 with the proper torque. By rotating adjusting screw 6, it is possible to adjust the resonant frequency.
This band-stop filter, however, has problems because the cost of machining screw holder 9 is high and the height of the screw holder 9 requires space.